The present invention relates to an adsorbent for the vapor of alcoholic fuels usable for canister etc. of vehicles using alcohol as a fuel.
Recently, vehicles driven with fuels mixed alcohols such as methanol and ethanol low in the emission of black smoke and nitrogen oxides with gasoline are attracting an attention.
As the adsorbent for canister of gasoline fuels, pulverized or granulated active carbon is used widely. But, because of low collection efficiency for alcohols, active carbon is unsuitable as an adsorbent for the vapor of alcoholic fuels.
An adsorption device for evaporated fuels provided with two adsorbent layers was proposed in Japanese Unexamined Patent Publication No. Sho 59-226263. Here, the provision of the second adsorbent layer comprising a material adsorbable polar components is described. It teaches that zeolite is also effective as a material suitable for the second adsorbent layer. However, no explanation is made about the type and characteristics of the optimum zeolite for this purpose. Commonly, the general purpose zeolite exhibits a strong adsorptive power up to low concentration region for water and alcohols being polar molecules. For this reason, if contacting this with the vapor of fuels containing polar molecules of moisture or alcohols, the polar molecules are captured intensively by zeolite. In the case of canister, the desorption of evaporated fuels adsorbed onto adsorbent is performed by introducing fresh air to adsorbent bed, that is, the adsorption and desorption are made through the difference in partial pressures. However, the polar molecules once adsorbed intensively onto the general purpose zeolite cannot be desorbed only through the difference in partial pressures at a level of the fresh air having been introduced to adsorbent bed. For this reason, the effective adsorption level is low when used as an adsorbent for vapor of alcohols.
As described, only by simply combining the adsorbents known hitherto, no satisfiable performance can be achieved for the adsorption and desorption of the vapor of alcoholic fuels, and there have been no suitable adsorbents intended for the alcoholic fuels until now.
The invention provides a zeolite-based adsorbent which exhibits an excellent adsorptive performance for the collection of the vapor of fuels containing alcohols.